A novel pulsing system was constructed at the Electrotechnical Laboratory. The system generates pulse trains of slow positrons of ～150 psec in duration ; the number of pulse trains is ～10⁵／sec. With the present system, we can measure lifetimes of positrons in matters with high counting rate, high peak-to-background ratio, and high time-resolution in very wide time-range. Also we can obtain information of defect properties of matters as a function of depth, because the incident energy of positrons can be abjusted from 0.4 to ～30 keV. Examples of lifetime distributions taken with the present system are shown together with discussion deduced from them.

  Intense pulsed slow positron beam has been produced using the 100MeV electron LINAC of JAERI・Takai. In order to use the beam for surface studies such as positron diffraction and positron microscopy, it was transferred from the solenoid magnetic field to field free region and then was brightness-enhanced. The beam size was reduced from 10mmφ (in the magnetic field) to 0.5mmφ after two stages of re-moderation. Using the intense brightness-enhanced positron beam we have observed for the first time RHEPD (Reflection High-Energy Positron Diffraction) patterns. A design of re-emission positron microscopy is also described.

  A new slow positron facility using electron linac has been designed and constructed at ISIR in Osaka University. In order to decide the size of converter and moderator and their relative position, EGS4 Monte Carlo simulation code was mainly used. This procedure and the result of preliminary experiment are presented.

  A new slow-positron source is under construction at the Photon Factory. Positrons are produced by bombarding a tantalum rod with high-energy electrons ; they are moderated in multiple tungsten vanes. Slow-positrons more than 10⁹ e⁺／s may be obtained with an electron energy power of 30k W.

  We report on the construction and operation of a monoenergetic slow positron beam apparatus in ultra-high vacuum. Positrons emitted from a ²²Na source are thermalized by a venetian-type vane consisting of well annealed W-foils with a thickness of 25.4μm. A source chamber and a specimen chamber are placed at a distance of 3.5m apart in order to reduce back ground radiation. Obtained slow positrons were guided by a magnetic field (～100Gauss) through multiple discrete acceleration lenses. Acceleration of slow positrons is performed by applying a high voltage between 0 and 30keV to the source chamber. Doppler broadening profiles of the annihilation radiations were measured by a Ge detector as a function of incident positron energy. The monoenergetic positron beam technique has been proved to be sufficiently sensitive for the detection of defects in the subsurface region.

  The positron beam facility using radioactive source in Nippon Steel Corporation is described which provides about 50,000 e⁺／s with the diameter of 5mmφ. The design criteria is explained and the beam performance obtained is shown. The source is 30mCi sodium-22 and a W mesh is used as a moderator. The positron beam is magnetically confined and the unmoderated positrons are removed by the cylindrical ExB filter. The energy of the incident positron can be changed from 100eV to 50keV. The beam shift dependent on the energy is compensated by a pair of stering coils. The application and the feasible improvement in future are given.

  The Japan Atomic Energy Research Institute, JAERI, has been promoting technical surveys for the “Positron Factory”, in which linac-based intense monoenergetic positron beams are planned to be applied to advanced materials characterization and new fields of basic research. A tentative goal of the beam intensity is 10¹⁰ s^-1, which is assumed to be realized with an electron linac of 100kW class with a beam energy around 100 to 150MeV. We performed a survey study on the dedicated linac in cooperation with four linac manufacturers. It confirmed technical feasibility of manufacturing the state-of-the-art linac. We have been carrying out a design study of the target (electron／positron converter and positron moderator). A new concept of the slow beam production system is demonstrated, which is expected to supply such intense beams for multiple sites simultaneouly.

  The energy variable monoenergetic positron beam has been successfully used for the study of defects near surfaces／interfaces. There has been a big demand on a probe for lattice defects near surface／interfaces in materials engineering. The well defined and controlled surface／interface will provide a new source of high-performance materials. The characterization of surface／interface is a key requisite. Electrons, ions, photons, and so on have been successfully used as a probe of atomistic arrangements and element compositions near surface／interface. More important is the defect analyses near surface／interface. We have had no suitable probe for defects until the physical process to create slow and／or monoenergetic positrons was discovered. This excellent feature of slow positron beam has attracted the interests of industrial people especially in semiconductor based devices. In the present article, the recent activities of the positron group at University of Tsukuba by means of a radioisotope based slow and／or monoenergetic positron beam are shown with the special emphasis on (1) defects induced by ion implantation in semiconductors, (2) the interface states in SiO₂／Si, (3) the creation of defects associated by the doping of impurity atoms into compound semiconductors, and so on.